Slow down there, Hercules! After 300 crunches, you might feel the burn in your abdominal muscles — but you probably haven't burned that many calories. The sad news is that crunches just aren't a big calorie-burner, particularly when compared to other physical activity.
However, if you're looking to build up a sweat and burn calories, cardiovascular activity that uses the large muscle groups to raise your heart rate is a much better use of your time.
Calories Burned Crunching
The average person completes about 30 crunches in one minute, meaning it'll take you about 10 minutes to complete your 300 crunches. Exactly how many calories you burn in this time depends on your size and the intensity of your crunches.
If you weigh 150 pounds and it's a moderate challenge to pump out your 300 crunches, expect to burn about 50 calories. Even if you work at an intense speed to get the exercises done and it takes half the time, you'll experience the same caloric burn. You just worked harder for five minutes.
Heavier, deconditioned people will burn more calories doing 300 crunches. If you weigh 250 pounds, for example, you'll burn 85 calories in 10 minutes of crunches working at a moderate intensity. If doing these crunches constitutes a vigorous intensity that leaves you sweaty and breathless, you'll burn approximately 150 calories in the 10 minutes.
Don't Crunch for the Caloric Burn
The extra calorie burn of crunches is nice, but it certainly isn't enough to bring about significant weight loss. You must create a caloric deficit of 3,500 calories to lose one pound.
Crunches strengthen the muscles of your middle — mostly the rectus abdominis, which forms the ridged six-pack envied by so many. The obliques at the sides of the waist assist each time you crunch. While working these muscles doesn't burn a lot of calories, it provides valuable strength to your core.
Performing 300 crunches in a row might be excessive, as you'll likely lose focus as you fatigue and, consequently, your form suffers. Too much repetition of the crunch movement can also lead to injury or pain in the neck or back.
Instead of going for volume, go for quality. Move slowly through each crunch and feel the action of pulling your belly button in toward your spine as you lift your torso skyward.
A Complete Core Routine
Augment crunches with other core moves to build a balanced, stable and strong middle. Do the following moves, in addition to a set of 10 to 20 crunches, as a circuit — one exercise after the other — with little rest to maximize calorie burn.